hm, special advice..? that’s a tough one, really. i don’t hate OCs, even hetalia, so i don’t get why other people hate them.
well, okay, i do. but here’s what i would go with, considering i’m not certain what your breed of HetaOC would be.
don’t make state OCs. it’s just… a little jarring. there are stereotypes for all of them, certainly, but it doesn’t really feel like there’s enough people for it to coalesce into a proper personification. you know? same with provinces and any other methods of dividing countries up into more manageable slices.
think about their appearances, too. maybe we’re reading too much into himaruya’s work, but that’s alright! OCs need to be well thought out with a reason for everything, and the more detail you have (which shouldn’t be infodumped, mind you) the better the OC will seem in comparison. for example, let’s take america and england, some of the most popular characters and the easiest for me to think of off the top of my head. we tend to be stereotyped in foreign media as being blonde with blue eyes- boom, america. england seems to be portrayed as blonde a lot too, but he has green eyes (and, temporarily, highlighter hair, but that’s studio DEEN than anything else). why? well, from what i’ve seen, green eyes seem to be associated with magic. the septimus heap series, for example, although harry potter seems to be the most popular. this is just a very simple overview, but it takes a surprising amount of research for some of the countries that aren’t portrayed in the media as often.
give them a personality! all the existing nations do. italy is ditsy, but not an idiot like the fandom makes him out to be (he can be, but these are moments, not the major characteristic), is somehow not as good of a flirt as his younger brother seborga… i could go on, but i’m pretty sure therantinghetaliachick has probably done a review on him, and since she’s still in the fandom (and i was always more familiar with romano, anyways), she can probably explain it a lot better than me.
actually, you know what, check her out. she’s done extensive discussions about OCs, so go through her archives for additional pointers. if you’d really like my opinion, you can send me a description or something and i can check them out, whether privately or not. just specify; i’d be happy to either way. hope this helped!